Heat the oil over medium-high heat in a large nonstick saucepot or Dutch oven. Add the sausage, onion, bell pepper, and garlic. Cook over medium-high heat, stirring occasionally, until the sausage is crumbled and browned, 8 – 10 minutes.
Add the broth, tomato sauce, diced tomatoes, salt, and crushed red pepper. Bring to a boil. Reduce the heat and simmer, stirring occasionally, until the flavors are blended, about 20 minutes. Add the noodles; bring to a boil. Reduce the heat and simmer, uncovered, stirring occasionally, until the soup thickens slightly and the noodles are tender, 10 – 12 minutes. Remove from the heat; stir in mozzarella, basil, and the Parmesan. Serve with the breadsticks, if using. (whole-wheat lasagna noodles take a little longer to cook.)
Recipe by The Taste Place at https://www.thetasteplace.com/healthy-hearty-lasagna-soup/